Safety switch



Das. 22, w42 A. E. @ADMAN SAFETY SWITCH Filed Sept. 25, 1939 PatentedDec. 22, 1942 SAFETY lSWITCH Addi B. Cadman, Beloit, Wis., assignor toWarner Electric Brake Manufacturing Company, South Beloit, Ill., acorporation of Illinois Application September 25, 1939,'Seria1 No.296,389

(Cl. Zoll- 52) 7 Claims.

The invention relates to a novel form of ysafety switch which isparticularly adapted for use to effect the automatic closure of a brakeenergiaing circuit in a trailer in case the draft connection between thetrailer and its tractor is broken.

Generally stated, it is an object of the invention to provide animproved switch suitable for the purpose indicated, which is simple,compact and rugged in construction, and which may be mountedconveniently on any character of trailer and yet will operate reliablyunder emergency conditions.

The invention also resides in the novel structure for carrying out theforegoing object.

Further objects and advantages of the invention will become apparent asthe following description proceeds, taken in connection with theaccompanying drawing, in which Figure 1 is a generally schematic planView illustrating the application of a switch embodying the invention ina trailer brake system.

Fig. 2 i-s an enlarged side elevation of the switch and its associatedparts with the switch in longitudinal section.

Fig. 3 is a longitudinal section of the switch similar to Fig. 2 butshowing the switch contacts in closed rather than open position.

Figs. 4 and 5 are transverse sectional views along they lines 4-4 and5-5 in Figs. 2 and 3 respectively.

Fig. 6 is a detail perspective view of a snap spring included in thetension-released actuating connection for the switch.

While the invention is susceptible of various modications andalternative constructions, I

have shown in the drawing and will herein describe in detail, thepreferred embodiment, vbut it is to be understood that I do not therebyintend to limit the invention to the specific form disclosed, but intendto cover all modications and alternative constructions falling withinthe spirit and scope of the invention as expressed in the appendedclaims.

Referring more particularly to the drawing, the invention has been shownherein as embodied in a switch, designated generally by the numeral III(Fig. 1), applied to the emergency energizing circuit for effectingapplication of electric brakes I2 on the wheels I2a of a trailer l I.The brake system may be of any suitable form of which many are wellknown. Current for effecting normal application of the brakes I2 issupplied through conductors I3, normally connected to a source ofcurrent (not shown) on the tractor I4 through a coupling, generallyindicated at I5, and under the control of a suitable switching mechanism(not shown) in the tractor.

The function of the improved safety switch I0 is to apply the brakes I2by connecting the leads I3 automatically to a supplemental source ofcurrent on the trailer, shown as a battery I6, in case 4the draftconnection (not shown) between the trailer and the tractor I4 isinterrupted unintentionally. For this purpose, one of the conductors I3is permanently connected to one battery terminal by a lead Il, while theother connector is connected to the other battery terminal through leadsI8 and I9 with the normally open switch I9 interposed between them.Consequently, when the switch I9 is closed, in a manner which willhereinafter appear, in response to rupture of the draft connection, thebattery I9 energizes the brake mechanisms and causes the trailer to bestopped automatically, thus insuring safety of operati-on.

In the instant embodiment (see Fig. 2), the switch l0 includes a casingmade up of two opposed cup-shaped sheet metal sections 23 and 2ldimensioned to t in telescoped relation as shown and held together byone or more screws 26. At their junction, the sections are apertured toreceive a cable |89 housing the conductors IS and I9. For convenience inmounting on the trailer, the section 2D is hung from the eye 22 of abolt projecting through the wall or other part at the front of thetrailer and clamped thereto by nuts 22a. The eye 22 interlocks with aloop 23 welded t-o the closed end of the casing section 26.

Slidable within the casing is an insulating member 25 composed of twodisks 25"JL and 25b rigidly connected together by a plunger 32 oi a formdescribed below. A second insulating member 24 is positioned in theopposite end of the casing where it is held by a screw 23. Twoshouldered contact pins 2l project through holes in the member 24 onopposite sides of its axis and are riveted to the member in clampingengagement with the terminal ends of the conductors I8 and I9. Aninsulating washer 30 covers and protects the butt ends of the pins andbared portions of the conductors.

The rounded projecting ends of the pins aline with holes 34 and 34a inthe member 25 and project part-way into the holes 34 when the insulatingmembers are axially separated as shown in Fig. 2. The ends are adaptedfor engagement with a resilient split contact ring 28 encircling a hub25 on the disk 25a. The ring 28 is of a diameter slightly less than theoverall spacing of the pins 21 so that when the member and good contactbetween the pins and ring isalways insured despite inaccuracies indimensioning or location of the parts and despitethel fact that, asshown, even less..thantl1reepinsV be used.

Actuation of the switch I0, in response to .part-1V` ing of the trailerdraft connection is accomplished by means of a plungery 324 slidable'ina` central aperture 35 (Fig. 2) in the stationary` The inner end of theplunger is insulator 24.-. shouldered to receive the disks 25a and 25vbwhich are held by a rivet head 33 formed on the plunger. The other endci the plunger projects through anaperture 3l .in the end of the. casingsection 2|l and its outer end is fashioned to. provide an enlarged head3S. cooperating with asnap spring 39 to form a tension-releasable'connection between th'e plunger and a chain 39W (see Fig.` 1)! anchoredon a rear bumperof the tractor I4.

The snap spring.39 is Afashionedfrom a piece of resilient wire havingits ends bent inloop form,-

as indicated at 3SZL (Fig. 6) 'and dimensioned .to engage the plunger!head 38 (Fig. 2) and form a sockettherefor.' When the trailerdr'aftconnection is intact, the chainhangs slack. Upon parting of the draftconnection, however, the chain is, of. course, jerked taut, therebyypulling theplungeri38outwardly from the l position of Fig. 2 to that of.Fig. 3 `so that the switch. con. tacts 21 are bridged. Furtheroutward..mot'ion,.-

of the. plungeris blocked, however, by the engagement oi theinsulatingmembers .24 and-25.

Accordingly, the increased tension on a chain39b.

causes the spring loops 39'@ to ride-up on the tapered inner end face38a ofthe plunger head and thereby separate so as to free .the head 158from its socket.. matically .actuated to closed positonand thereaftercompletely disconnected from'. the `tractor I4.

To ihcld the plunger .32.Yreleasably'in either`V In this way," theswitch is auto# open or closed position, aU-shaped spring clip or detentl0 (Fig. 5) is arrangedbetweenrthe.

casing end wall andlthe washer.` 3B (Fig.`3).

Cooperating ,with this detentspring is an en-- largement di. on'theplunger shank presenting oppositelytapered faces 4.5 and 46.. When theswitch is in its open position.(Fig. 2), the spring il engages the outerface 45 and yieldably re. sists outward movement of the '.plunger.: How'ever, when the plunger is pulled outward to the position of Fig. 3 inorder to closethe switch,

the spring 4i) rides over the enlargement 4I and' bears against theinner tapered face of the latter so as to hold the switch in closedposition; Ad-

ditionally, as the spring arms rideidown .this` inner face of theenlargement 4I, they tend to urge .the plunger 32 4outward .so as toinsure complete and effectual closing of the switchcontacts. The detentspring 40 is made weaker than the spring clip 39 so that upon anapp1ication of tension to the chain 39h, the detent will always bereleased for. closing of the switch prior tothe disengagement ci thespringlclp from' 'the -plunger head.

The detent for holding the plunger 32 alternatively in open or closedposition, as described above, also aids in maintaining a water-tightseal for the end of the switch casing through which the plungerprojects. The only movable part projecting from the switch casing is theplunger 32 so that the only point at which sealing difliculties arelikely to beencountered is at the casing aperture 31. through .which theplunger extends. Water-tight sealing of this aperture is, however,important because when traveling along a road in wet weather, water islikely to be splashed over the switch, and if it were permittedto enterthe same it would short .circuitfit, .thusapplying the trailer brakesand possibly causing a serious accident. Such a seal may be formed by ayieldable rubbed washer 42 (Figs-2 JandB) encircling the plunger betweena shoulder.43 thereon and the end wall of the casing. The thickness ofthe washer 42 is so proportioned. relative to thespacing of theshoulder. 43 'from the casingend wall that it will be compressed againstthe latter, effectually closing the aperture 3T when the plunger'is inits retracted position. Since the detent spring 40 urges theplungerinward in such case, the sealing washer 42 is retained firmly seated intight sealing. engagement.

t will be apparent that the improved safety switchis simple inconstruction and very reliable in operation primarily because therelative mo tion between the contact members to closethe switchis inthesame directionas the relative motion between the tractor and trailerwhich is the occasion for closingr the switch.` For this same reason,thesafety switchmay be suspended from the trailer vehicle and mounted'conveniently in any of the diierent locations encounteredfinservice,.but regardless of the location yof its mounting, the .switchwillbe closed reliably `when an .emergency arises.

I claim as myinvention:

l. In a switch of the type described, the combination of spacedgenerally. parallel Contact pins, an insulating support therefor, abridging contact for said pins in the .form of a resilient split ringnormally spacedfrom the outer ends' 4 into tight electricalcontacttherewith.

2. A switchl comprising, in combination, an insulating member having a:generally annular groove in its periphery, a resilient split contactring seated in said groove, said insulating member having an aperturetherein extending axially of the ring and opening into the root portionof.

tionsthereof, one of said members being xedly mounted and the .otherbeing movable toward and away .from said fixed member .into and out ofcontact-closing position, a plunger -flxedpn when said members are incontact-closing position serving to limit the endwise movement of saidplunger, whereby said connection is released upon application ofsufiicient tension thereto after said contacts are closed.

4. In a switch of the type described, the combination of a pair ofopposed rigid members having mounted on one of said members a set ofcontact rprongs projecting axially toward the other member and a splitring bridging contact on such other member positioned to embrace andresiliently engage 'the nose portions of said prongs when said twomembers are brought together, one of said members being fiXedly mountedand the other being movable toward and away from said fixed member intoand out of a limit contact-closing position,a plunger xed on saidmovable member and projecting toward and beyond said fixed member, meansfor releasably holding said members in spaced relation, and meansforming a tension-releasable connection with the free outer end of saidplunger releasable only upon the application of a force thereto greaterthan that required to release said biasing means, movement of saidmovable member to contact-closing position causing release of saidconnection upon application of sufcient tension thereto after saidcontacts are closed.

5. A switch mechanism of the character described having, in combination,a casing, two insulating members in said casing, one xed and the othermovable toward and away from the xed member, an actuating elementconnected to and movable with said movable member and projecting throughsaid casing, a contact on one of said members, a cooperating contact onthe other member engageable with said rst mentioned contact uponmovement of said members toward each other, detent means acting to holdsaid movable member releasably in switchopen and switch-closedpositions, and a coupling connected to the outer end of said element andreleasable automatically under tension applied thereto followingmovement of said movable member from one of said positions to the otheragainst the action of said detent means.

6. In a switch, the combination with a pair of contacts comprising aresilient split ring and a prong disposed generally normal to the planeof the ring with its nose pointed toward the ring and offset slightlyfrom the center line of the ring toward the center of curvature of thering, of means supporting said prong and ring for relative movement in adirection axially of the ring to bring to said prong and ring intorubbing engagement with the prong contacting the inner side of the ring.

7. 1n a switch, the combination with a plurality of relatively movablemembers including a pair of contacts shiftable relative to each otherbetween open and closed positions, and an actuator therefor., of meansincluding a strain-releasable coupling between said actuator and atleast one of said members for disconnecting the same after said actuatorhas been shifted a predetermined distance to move the switch contactsfrom one to the other of their said positions.

ADDI B. CADMAN.

